U.S. Pat. No. 6,845,126 B2 relates to a system for an adaptive antenna impedance matching. The impedance mismatch is determined dynamically by measuring the strength of a signal reflected from an antenna. An impedance matching circuit being electrically connected within the signal path is tuned in order to minimize the Voltage Standing Wave Ratio (VSWR). Tuning can be done by varying the reactances of different reactance-elements being electrically connected within the impedance matching circuit.
FIG. 1a shows a simple embodiment of a well known pi-section impedance matching circuit. A source impedance S is electrically connected in series with a signal path SP. An inductance element IN1 is electrically connected in series within the signal path SP, a capacitance element CP1 connects a contact of the inductance element with ground and another capacitance element CP2 connects the other side of the inductance element with ground. The three reactance elements CP1, CP2 and IN1 form the pi-section and are adjustable independently.
FIG. 1b presents a Smith-diagram showing the impedance of the above mentioned matching circuit. The desired value, e.g., 50 Ohms, is at the center of the diagram containing groups of curves exemplarily representing the total impedance depending on the value of the reactances of all three reactance elements. Variation of only one reactance limits the impedance to a circle-like subset of the whole area of the Smith-diagram.
Thus, it is obvious that dynamically finding a correct setting for all three elements that satisfies a given specification concerning the desired total impedance is not trivial. Algorithms to find the best setting are therefore not straightforward but may base on lookup-tables and are complex and prone to errors.
Therefore, what is needed is an impedance matching network with improved design to work with a straightforward and unambiguous algorithm.